1. Field of the Invention
This invention relates to a low-noise level automotive internal combustion engine, and more particularly to an engine equipped with a bearing beam structure for supporting a crankshaft.
2. Description of the Prior Art
One of the major sources of engine noise is vibration noise emitted from the cylinder block skirt or lower section and oil pan of the engine. This noise is caused by the vibration of the cylinder block. In order to reduce such vibration noise it would appear to be sufficient to suppress vibration due to explosion torque applied to the crankshaft by increasing the rigidity of the cylinder block. However, this unavoidably leads to an increase in cylinder block wall thickness and accordingly to a great increase in engine weight, thereby giving rise to new problems such as reduced fuel economy. In view of this, a variety of proposals have been made to improve the rigidity of the cylinder block while suppressing an increase in cylinder block weight. In these proposals, particular attention has been paid to the employment of a bearing beam structure which securely connects a plurality of bearing caps for directly supporting the crankshaft to improve the strength of bearing caps and engine parts associated therewith.